If $x \boxdot y = 3x-4y$ and $x \bigtriangledown y = 4x-y$, find $-1 \boxdot (1 \bigtriangledown -5)$.
Explanation: First, find $1 \bigtriangledown -5$ $ 1 \bigtriangledown -5 = (4)(1)-(-5)$ $ \hphantom{1 \bigtriangledown -5} = 9$ Now, find $-1 \boxdot 9$ $ -1 \boxdot 9 = (3)(-1)-(4)(9)$ $ \hphantom{-1 \boxdot 9} = -39$.